1. Field of the Invention
The present invention relates to a vehicle power-generation control unit capable of performing gradual excitation for a vehicle generator.
2. Description of Related Art
As disclosed, for example, in Japanese Patent Application Laid-open No. 3-60338, there is known a vehicle power-generation control unit configured to gradually increase the exciting current of a vehicle generator when the output voltage of the vehicle generator drops as a result of application of an electrical load. With this vehicle power-generation control unit, it is possible to avoid abrupt lowering of a rotational speed of a vehicle engine, because, even when the output voltage of the vehicle generator drops abruptly as a result of application of an electrical load, the duty ratio of the exciting current flowing through the exciting winding of the vehicle generator is increased only gradually in order to avoid abrupt increase of the power generation torque.
There is also known a vehicle power-generation control unit configured to perform such a gradual-excitation control only for continuous electrical loads, and not for intermittent electrical loads such as a turn signal lamp and a hazard flasher as disclosed, for example, in Japanese Patent Application Laid-open No. 5-260679. This vehicle power-generation control unit makes it possible to avoid fluctuation of the output voltage of the vehicle generator, which can occur if the gradual excitation control is performed for the intermittent electrical loads, to thereby avoid the occurrence of brightness fluctuation of the turn signal lamp or hazard flasher. Determination whether an electrical load applied is a continuous load or an intermittent load can be made, for example, on the basis of the output voltage of the vehicle generator. In addition, this vehicle power-generation control unit has a capability of changing a gradual excitation time (the time span during which the duty ratio of the exciting current is gradually increased).
Since the increasing rate of the output power of the vehicle generator when the exciting current is increased gradually depends on the temperature and the rotational speed of the vehicle generator, it is also known to adjust the increasing rate of the duty ratio of the exciting current in accordance with the rotational speed and the temperature of the vehicle generator, as disclosed, for example, in Japanese Patent Application Laid-open No. 2002-204600.
However, the vehicle power-generation control unit disclosed in Japanese Patent Application Laid-open No. 3-60338, in which the increasing rate of the exciting current is constant, has a problem in that a terminal voltage of a vehicle battery (may be referred to as a battery voltage hereinafter) can be lowered excessively, and the engine speed can become unstable depending on the magnitude of an electrical load applied.
Also, the vehicle power-generation control units disclosed in Japanese Patent Applications Laid-open No. 3-60338, No. 5-260679, and No. 2002-204600 have a common problem in that the engine speed can become unstable and the battery voltage can be lowered excessively depending on a vehicle state (an engine torque state, for example) when a large electrical load having an inrush current such as an electric motor is applied.